This is an age in which the big clubs, in theory, just keep getting bigger. The Champions League is an elite world for elite sides. And yet somehow the two Milan clubs, with 10 European titles between them, have been absent from the competition since 2013-14. Given the money it has spent and the players it has bought, Inter’s struggles, frankly, have been hard to explain and such is the sense of sickness at the club that nobody can look to the future there with any degree of confidence.

For AC Milan, though, this summer’s activity has brought a distinct sense of a corner being turned.

That represents an extraordinary coup, one that is telling not just for what it means in terms of personnel but for what it means psychologically. This has already been described as a “reverse Pirlo.” In 2011, after a decade at Milan, Andrea Pirlo left for Juventus following a falling out with then-Milan coach Massimiliano Allegri. Juve has won every league title since.

Bonucci’s relations with Allegri, now Juventus coach, were strained last season, but, still, nobody expected this. That’s why the transfer has been greeted with such a sense of shock.

Bonucci is, arguably, the best central defender in the world. Antonio Conte was keen to sign him, but Chelsea gave up the hunt, apparently convinced Bonucci would not leave Juve. So what has happened?

It seems Milan made no real move for the defender. It had, after all, already brought in three defenders for $70 million. Rather, it was initiated by Bonucci’s agent, Alessandro Lucci.

Bonucci and Allegri argued throughout a 4-1 win over Palermo in February, leading Allegri to leave the defender out of the squad for the ensuing Champions League trip to Porto. When Juve won 2-0, it seemed Allegri had made his point and reasserted his authority. Bonucci returned to the side and took the captain’s armband for Juve’s following game. On the surface all seemed well, but beneath the animosity was still rumbling, reportedly erupting at halftime in the Champions League final, when Bonucci criticized Andrea Barzagli for his part in Real Madrid’s opening goal and also attacked Paulo Dybala.

Bonucci’s contract runs until 2021. Juve was under no compulsion to sell. If Manchester City is willing to pay $65 million for Kyle Walker, if Chelsea was willing to pay $40 million for Antonio Rudiger, who knows what price Bonucci might have reached? Certainly more than the $45 million Milan looks like it will be paying. All of which makes the transfer feel all the stranger.

It’s true that the move from a back three to a 4-2-3-1 means there is less call for central defenders, and Juve does have Medhi Benatia and Daniele Rugani as backup with Mattia Caldara to join from Atalanta next summer. It’s also true that Bonucci is now 30. But even if it had become impossible for Bonucci and Allegri to work together, it’s hard to understand why Juve would let him go for a comparatively reduced price to a side that could be a direct competitor next season.

For Milan, this is an ideal signing, a defender of proven quality who can pass the ball and has a history of winning, an experienced player and a leader who can galvanize an otherwise youthful squad. Even better, he perhaps has a point to prove to Juve. A deal to sign the Argentinian midfielder Lucas Biglia from Lazio should be completed soon, and there remains talk of another striker arriving at the San Siro.

Perhaps those are too many changes in one go for Milan to challenge seriously next season. It always takes time for players to gel, and manager Vincenzo Montella will effectively have a whole new side to piece together. Juventus, even without Bonucci, remains formidable and will go into the new season bolstered by the signing of Douglas Costa and quite probably Federico Bernardeschi.

But for the first time in a long time, Milan is back in the conversation, and, with four Italian sides to qualify for the group stage for the following season, it should be looking forward to a return the Champions League in 2018-19.

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